Particle Systems

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Particle Systems

• Particle Systems

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Particle Systems

• Simulate explosions, smoke, fire, spray
• Thin linear/cylindrical natural objects
• Particle physics
• First used for graphics in 1982 for Star
  Trek II The Wrath of Khan
• Genesis demo sequence

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Particle Life Cycle

• Small geometric object
• Each particle has a life cycle
• Each particle is independent
• Undergoes a random path controlled by probability
  distribution

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Basic Particle

• A small geometric object
• Initial position
• Initial velocity (both speed and direction)
• Initial size
• Initial color
• Initial transparency
• Shape
• Lifetime

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Particle Emitter

• Each particle will come from an emitter
• Has a number of particles
• Random number of particles/frame
• Randomize initial values of each particle

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Particle Collection

• Emitters at certain locations
• Fixed (Water spraying from hose)
• Distributed
• Designate emitters on surface or in 3D space
• Semi-random
• Designate center of emitter distribution
• Emitters randomly distributed about the
  distribution center

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Particle Physics

• F MA
• A acceleration (initial push, gravity, etc)
• V current velocity dt A Vprev
• X current position dt V Xprev

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Environmental Effects

• Could add
• Wind
• Magnetism, etc
• Global forces can be handled per particle
• Local forces need either equation or data
• Voxel field representing local wind velocities

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Envirnoment

• Collision Detection!
• Simple point-object collision
• Collision response
• Reflection (with energy loss)
• Absorption (sparks lose heat)
• Flow (water spreads out)
• Particle-on-particle O(N2)

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Data Management

• Preallocate a pool of particles
• Update each particle in pool

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Particle Rendering

• GL_POINT
• Single pixel point
• OK for slow particles
• Line segment
• Account for particle motion
• If frame-to-frame particle spacing gt 1 pixel
• Simulates motion blur

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Motion Blur

• Must account for temporal properties of animated
  object
• Simulate effect of film exposure during finite
  shutter opening time

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Example Wrath of Khan
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Grass Simulation
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Particles in Games

• 2 triangles (4 vertices)/particle
• Large semitransparent particles for smoke
• Textures

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Particle Shape

• Texture
• Blend
• Distort

Sparks Flare
Animated Texture
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Lightning

• Create a tree for lightning path
• Drive particles along branches
• Load texture once for entire effect

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Rain

• Rainfall Stretched shape
• Impact Spark splatter